Numerical Study on Flow Capacity of the Bottom Axis-driven Overflow Weir

A kind of bottom axis-driven overflow weir is extensively applied to improve hydrodynamics of urban rivers in plain areas of China, which is considered superior fit and high integration with the urban water environment. It is a new kind of hydraulic building, which can get different head difference and discharge by adjusting opening. The flood discharge and navigation will not be affected when it completely lies down (opening degree 0°), and a small water fall landscape will be formed when opening degree is adjusted between 0°-90°. In this paper, κ-ε turbulence model is applied to obtain the flow parameters such as discharge characteristics, velocity distributions, streamline, and water surface profiles. The volume of fluid (VOF) scheme is used to find the free surface. The predictions of the proposed numerical model are validated using existing experimental data and theoretical expressions of opening degree are 0 °and 90°. A properly validated model permits one to obtain the hydraulic parameters of bottom axis-driven overflow weir at different opening (75°, 60°, 45°, 30°, 15°) without recourse to expensive and more time consuming experimental methods. The main conclusions of this research are as follows: ①The flow coefficient increases firstly and then decreases during the change of opening degree from 0°-90°, and the flow coefficient at 0° is less than that at 90°opening degree. ②The relationship between opening degree and flow coefficient becomes more unstable as well as smaller water head. ③Both the water head and the opening degree are supposed to certain influence on the overflow capability of the bottom axis-driven overflow weir. But the influence of the water head is more complicated.